A well-known construction of spray pumps for spraying cosmetic liquid, insecticide, washing liquid and other home spray liquid has two pistons of different diameters and serially coupled to each other, that is, with the small piston coupled before the large piston. The large piston has a valve adapted to be closed in the direction of supplying liquid, while the small piston has a valve adapted to be opened only in the direction of supplying liquid. Further, the small piston is spring biased so that it is normally held at its dead point.
Generally, the subject matter of these spray pumps have a number of times the discharge capacity of other well-known spray pumps of the same three-dimensional size. Also, they permit spraying of liquid under a high stored liquid pressure without the necessity of quickly or slowly depressing the pump piston with a finger, that is, irrespective of whether the piston is depressed with high or low finger pressure, thus permitting a finely atomized liquid spray pattern by a high pressure jet to be obtained. In case of the insecticide, these features can meet the requirement for the atomized liquid particles to float in space for a long period of time so as to obtain enhanced insecticidal effects. Also, in case of cosmetic liquid or the like they can be utilized as means for providing fine liquid particles which are required since it is desirable that the sprayed liquid quickly forms a thin film.
Regarding the structure of the small piston in these spray pumps, the small piston is disposed below the large piston or concentrically disposed within the large piston or has other structures. In any case, it is arranged such as to receive liquid pressure increased by the large piston and be displaced by the received liquid pressure so as to open a valve which is normally closed in the direction of supplying liquid, thus permitting liquid under increased pressure to be sprayed from a nozzle button connected to the top of the cylinder. However, the small piston tends to be too sensitive to the liquid pressure received from the large piston, so that the valve of the small piston is liable to be actuated before the liquid pressure is sufficiently increased. In such case, the effect that can be provided by the subject liquid in this type of spray pump cannot be satisfactorily obtained. Besides, in these spray pumps the individual component parts are assembled within a small space, thus requiring high precision in manufacture. Further, the component parts are large in number and are complicated, so that the construction is readily prone to trouble.
The spray pump according to the invention can control or suppress too sensitive action of the small piston without sacrifice in light and smooth operation and permits displacement of the small piston only under a sufficiently increased liquid pressure so that the effects which are to be provided by this type of spray pump to be obtained sufficiently and reliably. In addition, its construction is simplified by providing individual pistons of different diameters whithin a single cylinder consisting of different diameter portions. Further, a sudden end can be brought to spraying as soon as the last stage of downward stroke of piston is reached.